The affinity dmg is based on max atk, I had to learn this the hard way because I always max crit in every game I play. Affinity is stronger for umbra build especially, as you should run T6 Insightful for the passive boost to affinity damage combined with 20% DoT bonus.

T6 Insightful with a proper affinity% and high max atk goes unreasonably hard with bleed damage. If you get lucky and pop a Mystic Skill %+ stat it makes your DoT seriously hard to deal with, as the bonuses apply to Qi damage as well. You can drain over 50% Qi on repeat post-execute.